1. Field of the Invention
The present invention relates to an electrical connecting structure and a electronic device bonding structure, and particularly relates to a low stress connecting structure and a bonding structure which using this structure.
2. Description of Related Art
As technology advances, all kinds of electronic devices are developed to be miniaturized and multi-function. Hence, high density assemble methods were developed to increase electrical signal transition.
By conventional technique, anisotropic conductive film (ACF) is a popular connecting method using for electronic components connection such as semiconductor with the patterning electrodes of ITO glass. ACF is placed between semiconductor and ITO glass. And then, apply pressure and temperature on the semiconductor, ACF and glass. Semiconductor and ITO glass will be electrically connected by way of ACF which contain of conductive particles inside.
However, when the density of electrode of semiconductor and ITO glass continue increasing, gap between the electrodes will be decreased. As a consequence, ACF conductive particles may be gathered in space between two electrode, and cause short circuit or electric leakage.
Another assemble method was developed to solve this problem. Its electrode structure is made by polymer and surface is covered by metal. Non-Conductive film (NCF) or Non-conductive paste (NCP) is used for semiconductor device joining with device carrier. After applied pressure and temperature on semiconductor, the polymer electrodes which attached on semiconductor surface will be passing through non-conductive film and contact the electrode where on the device carrier. Electrical connection will be connecting by the metal layer where cover on the surface of polymer bump. Also, non-conductive film is epoxy base material which can provide permanent mechanical supporting to maintain the electrical connection. However, Young's module between polymer bump and metal cover layer has large difference. This will cause the problem of stress concentration on the metal layer, result in metal layer broken and affected its electrical reliability.
To solve the above problem, U.S. Pat. No. 7,170,187 provides a method, which adds metal particles into the polymer bump. Also, metal structures are added onto the surface of the polymer bump or inside the polymer bump, so that the bump both has electrical conductivity and elasticity property. However, to apply such a method, developing special metal particles is necessary. Furthermore, adding metal structures on the surface of the polymer bump or inside the polymer bump will lead to the process become more complicated.
In addition, U.S. Pat. No. 7,246,432 provides a method, in which the polymer bump is made of special polymer material. During curing, the special polymer will shrinking and form arc structure. Then, another polymer material layer and metal layer will cover on it sequentially. The disadvantage of this method is using curing process to build the arc structure is hard to control, bumping process also difficult and complicated.